Such devices are utilized for testing long guideways in machine tools and for determining angle deviations between the axes of parts of large machines. In this context, the device acts as an adjusting collimator whose collimating beam is observed with the aid of an appropriately configured telescope. If the collimating mark imaged by the adjusting collimator to infinity is so configured that it supplements a collimating mark in the telescope to a symmetrical figure, then deviations can be easily detected which occur during rough operation and can be measured by an appropriate calibration. Depending upon the type of machine, extreme mechanical and even thermal loads can be applied to the adjusting collimator.
A further advantageous application of such devices is the monitoring of the spatial position of the opening of the barrel of a weapon such as a cannon. For this purpose, the device is placed at the vicinity of the barrel opening and the collimating beam emitted by the device reaches a target apparatus. The target line of this apparatus is set at a precisely predetermined angle to the axis of the cold barrel during adjustment. For this purpose, an adjusting device is introduced into the barrel of the cannon as explained, for example, in German Patent No. 1,257,039. After adjustment is completed, the target beam of the device, running opposite to the direction of the projectile, reaches a predetermined position in the target apparatus with the device here being used again as an adjusting collimator.
The barrel becomes hot during the firing of the projectiles and can therefore bend so that the axis of the barrel opening which determines the flight direction of the projectile is changed with respect to its spatial position. This becomes manifest in a deviation of the collimator target beam from its desired position so that the target apparatus can be correspondingly readjusted. Thereafter, the target beam again takes on its correct position with reference to the axis of the barrel opening.
In the above application, the mechanical and thermal load on the adjusting collimator is especially large. Accordingly, forces develop in the region of the cannon opening which can even exceed 40,000 g.
U.S. Pat. No. 4,704,010 is incorporated herein by reference and discloses a device of the kind described above wherein a single-lens objective is mounted in a metal housing connected in a form-tight manner to the support. The single-lens objective has a first optical surface upon which an illuminated collimating mark is arranged and a second optical surface lying opposite the first optical surface. The central region of the second optical surface is provided with a reflective coating and the single-lens objective is made of a material having a linear coefficient of expansion of less than 10.sup.-6 .multidot.K.sup.-1. The single-lens objective is held in the housing in a form-tight manner with a layer of elastic material that permanently retains its elasticity. This layer surrounds the peripheral surface of the objective.
This device fulfills all requirements as to stability and reliability of the adjusted condition which result from extreme mechanical and thermal loading.
However, it has been shown that temperature changes lead to a deterioration of the imaging quality of the adjusting collimator which can become disturbing for high values of temperature difference.
This effect can be attributed to the condition that for the known device the actual imaging beam path in the collimator runs within a compact optical medium whose refractive power changes in dependence upon its temperature. In this way, inhomogeneities occur in the optically effective portion of the collimator in the presence of local temperature differences in the optical medium and these inhomogeneities diminish the imaging quality. Such local uneven temperatures in the optical medium occur because, even though this medium has an extremely low linear coefficient of expansion, it does have a relatively low heat conducting capability. For this reason, a uniform temperature develops in the optical medium of the collimator only very slowly when there is a temperature change of the base to which the device is connected.
A reduction in the imaging quality develops especially when the device is mounted in the region of the barrel opening of a cannon.